Prior to the present invention, convoluted boot seals of rubber and plastic materials for universal joints and other mechanisms have been designed with various constructions to control and enhance the action of the boot seal during the various geometric motions of the seal protected device. The boot seal disclosed in U.S. Pat. No. 4,456,269 issued to Werner Krude et al June 26, 1984, for example, is provided with web like external ribs interconnecting an end attachment collar to an adjacent convolution to reinforce and strengthen the boot seal. The disclosed boot seal further has radially inward projections which act as stop means when the joint is articulated toward its limits. In U.S. Pat. No. 4,702,483 issued to Mikio Ukai et al Oct. 27, 1987, a circumferential convex strip is provided on an inner surface of at least one of the convolutions of the boot seal to control the manner in which the seal collapses under certain operations to prevent the entrapment of convolutions between a first convolution and a drive shaft.
The present invention is of the general category of U.S. Pat. Nos. 4,456,269 and 4,702,483 cited above, but provides new and improved convoluted boot seal preferably of a suitable resilient plastic material with wall construction designed to increase wall strength to reduce wrinkling and to reduce wall to wall scrubbing for minimized abrasion and convolute root stress during the flexure action of the boot including the high angled stroking and rotational drive of an axle shaft with respect to a universal joint housing.
In the preferred embodiment of the invention the boot seal is blow molded from a thermoplastic material and the walls of at least some adjacent convolutions respectively have aligned and cooperative internal and external ribs formed directly therein. During action of the device protected by the seal, the cooperative ribs can mesh to limit sliding contact of adjacent convolution side walls to limit and transfer torsional load and reduce abrasion and wear of such walls as well as convolution root joint stress and thereby increase boot service life. These ribs also strengthen the walls of the convolution so that they will not wrinkle and crack under working conditions particularly at low temperatures which may range to -40.degree. F.
More particularly, the arcuately spaced external ribs are directly formed in the surface of one sidewall in an annular pattern and generally project toward the sidewall of an adjacent convolution. The sidewall of the adjacent convolution is formed with internal ribs directly therein providing corresponding recesses or spaces into which the external ribs of the first sidewall fit during certain boot seal flexure actions. This rib and the rib space engagement is similar to that of spur gear teeth. However, in the present invention, the rib space or lash provided by the side walls of the internal ribs can be varied to control the relative rotational movement between the sidewalls of the convolutions.
With a wide rib space, limited turning of one convolution side wall relative to the side wall of the adjacent convolution is provided so that torsional boot flexure loads can be distributed throughout the entire boot seal. The spacing for the ribs can also be such that there is substantially no relative rotary movement between the rib and the meshing rib space so that there is substantially no relative turning motion between adjacent large diameter convolutions so that torsional flexure loads are transmitted to different areas of the boot. Accordingly, with a "no lash" configuration, the relative turning of the convolution could be limited to the outboard small diameter convolutions which generally do not contact each other so that frictional wear of interfacing side walls throughout the boot seal is substantially eliminated.